There is much scientific interest in developing and validating biochemical (biomarkers) of total dietary fat intake. The major components of dietary fat are fatty acids and the various fatty acids are metabolized very differently in the body, depending on their structure. In addition, humans are capable of synthesizing monounsaturated and saturated fatty acids from a variety of substances, including carbohydrate and protein. Therefore, associations between tissue concentrations of fatty acids and dietary fatty acids are generally weak, apart from fatty acids that can not be synthesized in the body. One approach to identify potential biomarkers of dietary fat intake is to test compounds that are specific to fat in food, are not synthesized in the body and can be measured in body tissues. We have identified four such compounds that showed promising results in preliminary studies. Three of these are fatty acids--heptadecanoic acid (C17:0), trans-octadecenoic acid (9t-C18:1), and linoleic acid (C18:2 (n- 6)). The other is gamma-tocopherol. These compounds, together, are found in over 90% of the sources of dietary fat in the American diet. We will test these compounds in the context of a controlled, randomized, dietary intervention trial. Eighty, post-menopausal women will be randomized to consume a diet providing either (i) 18 % kilocalories (kcal) from fat (ii) 36 % kcal from fat. The women will be provided with all foods and will consume these diets for seven weeks. Blood, buccal (cheek) cells and saliva will be collected on two occasions, separated by seven days, at baseline and at the end of the study. The concentration of the three fatty acids will be determined in plasma phospholipids, red blood cells, buccal cells and saliva. Gamma-tocopherol will be determined in serum.